The purpose of this study is to compare the contribution of gluconeogenesis to hepatic glucose production of preterm infants given glucose alone vs. a combination of either glucose and amino acids, glucose and lipid or glucose, amino acids and lipid during the first 48 hours of life. The hypotheses to be tested are: 1) amino acids, lipid and a combination of both enhance gluconeogenesis in the VLBW infant and 2) substitution of IV amino acids, lipid or both for glucose diminish hyperglycemia without increasing the risk of hypoglycemia.